Experimental investigation of vibration pretreatment-microwave curing process for carbon fiber reinforced resin matrix composites

The vibration pretreatment-microwave curing process is an efficient,low energy consumption,and high-quality out-of-autoclave curing process for carbon fiber resin matrix composites.This study aims to investigate the impact of vibration pretreatment temperature on the fiber weight content,microscopic morphology and mechanical properties of the composite laminates by using optical digital microscopy,universal tensile testing machine and thermo-gravimetric analyzer.Additionally,the combined mode of Bragg fiber grating sensor and temperature measurement fiber was employed to explore the effect of vibration pretreatment on the strain process during microwave curing.The study results revealed that the change in vibration pretreatment temperature had a slight impact on the fiber weight content when the vibration acceleration remained constant.The metallographic and interlaminar strength of the specimen formed at a vibration pretreatment temperature of 80℃ demonstrated a porosity of 0.414% and a 10.69% decrease in interlaminar shear strength compared to autoclave curing.Moreover,the introduction of the vibration energy field during the microwave curing process led to a significant reduction in residual strain in both the 0°and 90°fiber directions,when the laminate was cooled to 60℃.

Kinetics of Thermal Decomposition of Lithium Hexafluorophosphate

With on-line coupled thermo-gravimetric technique, the thermal decomposition of analyzer-Fourier transform infrared spectrometer lithium hexafluorophosphate （LiPF6） and its gas evolution at inert environment （H2O〈10 ppm） were studied under both non-isothermal and isothermal conditions. The results showed that the LiPF6 decomposition is a single-stage reaction with LiF as final residue and PF5 as gas product. In addition, its decomposi- tion kinetics was determined as 2D phase boundary movement （cylindrical symmetry） under both non-isothermal and isothermal conditions. Furthermore, the activation energy of LiPF6 decomposition was calculated as 104 and 92 kJ/mol for non-isothermal and isothermal con- ditions, respectively.

Comparison of burn rate and thermal decomposition of AP as oxidizer and PVC and HTPB as fuel binder based composite solid propellants

In the present investigation an effort has been made to understand the thermal decomposition and burn rate characteristics of AP as oxidizer and PVC and HTPB as fuel binder in composite solid propellant. The burning rate study has been carried out at ambient and different pressures of 2.068 Mpa, 4.760 Mpa,6.895 Mpa. The mechanism of thermal decomposition of each composition have also been determined by NETZSCH simultaneous thermal analyser, comprising differential scanning calorimeter(DSC) and thermo-gravimetric analyser(TGA). An effort has been made to study the burn rate and decomposition of fuel binder and oxidizer in presence of Fe_2O_3 and also their overall impact on combustion of propellant.

The Effects of Stacking Sequence on Dynamic Mechanical Properties and Thermal Degradation of Kenaf/Jute Hybrid Composites

This research focused on the dynamic mechanical and thermal properties of woven mat jute/kenaf/jute(J/K/J)and kenaf/jute/kenaf(K/J/K)hybrid composites.Dynamic mechanical analysis(DMA)and Thermo-gravimetric Analysis(TGA)were used to study the effect of layering sequence on the thermal properties of kenaf/jute hybrid composites.The DMA results;it was found that the differences in the stacking sequence between the kenaf/jute composites do not affect their storage modulus,loss modulus and damping factor.From the TGA and DMA results,it has been shown that stacking sequence has given positive effect to the kenaf/jute hybrid composite compared to pure epoxy composite.This is because kenaf and jute fibre has increased the Tg values of the composites,thus affect the thermal degradation.Results showed that the storage modulus for kenaf/jute hybrid composites increased compared with pure epoxy composites with increasing temperature and the values of remained almost the same at glass transition temperature(Tg),the hybrid composite perhaps due to the improved fibre/matrix interface bonding.The preliminary analysis could provide a new direction for the creation of a novel hybrid composite which offers unique properties which cannot be accomplished in a single material system.

Reaction Kinetic Equation for Char Combustion of Underground Coal Gasification

Based on the quasi-steady-state approximation, the dynamic equation of char combustion in the oxidation zone of underground coal gasification (UCG) was derived. The parameters of the dynamic equation were determined at 900℃ using a thermo-gravimetric (TG) analyzer connected to a flue gas analyzer and this equation. The equation was simplified for specific coals, including high ash content, low ash content, and low ash fusibility ones. The results show that 1) the apparent reaction rate constant increases with an increase in volatile matter value as dry ash-free basis,2) the effective coefficient of diffusion decreases with an increase in ash as dry basis, and 3) the mass transfer coefficient is independent of coal quality on the whole. The apparent reaction rate constant, mass-transfer coefficient and effective coefficient of diffusion of six char samples range from 7.51×104 m/s to 8.98×104 m/s, 3.05×106 m/s to 3.23×106 m/s and 5.36×106 m2/s to 8.23×106 m2/s at 900℃, respectively.

Effect of Raw Bauxite Addition on Thermal Behaviour of Ultra-low Cement Al_2O_3-SiO_2 Castables

This work investigated the thermo-gravimetric （TG） change and explosion resistance of ultra-low cement Al2O3 - SiO2 castables added with 0, 5%, 10%, 15% and 20% of 474 μm raw bauxite powders containing 72.8% Al2O3, respectively. The castables were prepared using white fused alumina as aggregate, powders of white fused alumina, fused mullite,α-Al2O3 ultrafines, 3% CA cement and 5% microsilica as the matrix portion. TG change of the castables was investigated by a thermo-gravimetric analyzer for large size specimen. When the raw bauxite addition is less than 10%, the mass-losing behavior of the castables is similar to that without raw bauxite, tending to reach a constant mass around 400 ℃ , before which the mass-loss is mild and producing little destructive influence. With more than 10% raw bauxite addition, however, the mass-loss increases significantly, and the temperature to reach a constant mass increases to 600 ℃ or higher, unfavorable to structural stabilization. With the raw bauxite addition up to 20% , no negative influence on explosion resistance is found.

Study on Co-combustion Characteristics of Superfine Coal with Conventional Size Coal in O₂/CO₂Atmosphere

The pulverized coal combustion in O2/CO2 atmosphere is one of the promising new technologies which can reduce the emission of carbon dioxide and NOx. In this study, the combustion behaviors of different mixing ratio of Shenhua coal with 20 μm and 74 μm particle size in the O2/CO2 atmosphere and air atmosphere were studied by using a thermal-gravimetric analyzer. The combustion characteristics such as ignition and burnout behavior were investigated in the temperature from 20℃ to 850℃. The influence of mixing ratio on combustion characteristics was conduced. The results obtained showed that the ignition temperature of the two kinds of particle size in O2/CO2 atmosphere is higher than in the air, while the activation energy in O2/CO2 atmosphere is lower. With the increasing ratio of 20 μm superfine pulverized coals, the ignition temperature and the activation energy decreased, while the DTG peak value increased, the maximum burning rate position advanced. There were three trends for the ignition temperature curve with the increasing of superfine coal ratio: the ignition of the mixed coal decreased rapidly, then changed less, at last reduced quickly.

Intensification of bituminous coal and lignite oxidation by copper-based activating additives

The oxidation of lignite and bituminous coal samples modified by 5 wt%(in terms of dry salt)addition of copper salts Cu(NO_(3))_(2),CuSO_(4),and Cu(CH_(3)COO)_(2) was studied.The samples’reactivity was studied by thermogravimetry within a temperature range of 45–600℃ at a heating rate of 2.5℃/min in an oxidizing environment.The introduction of activating additives has resulted in a significant decrease in the temperature of intense oxidation onset(ΔT_(i)=20/94℃),in a reduction in the sample residence time in the volatile matter release region(Δt_(e)=2/22 min)and the total duration of the coal combustible mass oxidation(Δt_(f)=8/14 min).The Friedman method was used to calculate the activation energy values for the oxidation process of the modified samples.The maximum change in activation energy values was observed for the bituminous coal sample.The possible mechanism behind the action of the copper-salt additives,which activate the oxidation of lignite and bituminous coal,is discussed.According to the data of mass spectrometric analysis,the concentration of NOx in the reaction products decreases as the temperature of the activated oxidation process is shifted towards the low-temperature region.

Synthesis and Characterization of Pr(DPM)_3 Served as Precursor for MOCVD

Praseodymium β-diketone chelate, Pr （DPM）3 [ DPM = 2,2,6,6 -tetramethyl-3,5-heptanedionato ], was successfully synthesized from the inorganic salt praseodymium chloride and HDPM（2,2,6,6-tetramethyl-3,5-heptane-dione） in an ethanol/aqueous solution followed distillation at low pressure and recrystallization from toluene. The physical and thermal properties of the chelate, including volatility, stability, and thermal decomposition, were investigated by elemental analyses, 1^H NMR spectroscopy, XRD, TG/DTG/DTA analysis, infrared spectroscopy, and mass spectroscopy. The chelate with high purity prepared by the authors of this study also shows sufficient volatility and Stability in inert gases, which could be used as the precursor for metal-organic chemical vapor deposition（MOCVD）.

Synthesis, Characterization of Cellulose Grafted N-Oxide Reagent and Its Application in Oxidation of Alkyl/Aryl Halides

Oxidation of aliphatic and aromatic halides by N-oxide functionalities supported on 4- vinyl pyridine, (4-VP), grafted cellulose is reported in the present manuscript. Synthesis of graft copolymer of cellulose and poly 4-vinyl pyridine, poly(4-VP), has been carried out using ceric ions as redox initiator. Post-grafting treatment of CellO-g-poly (4-VP) with 30% H2O2 in acetic acid gives Cellulose-g-poly (4-VP) N-oxide, the polymeric supported oxidizing reagent. The polymeric support, CellO-g-poly (4-VP) N-oxide, has been used for oxidation reactions of different alkyl / aryl halide such as 1-bromo-3-methyl butane, 2-bromo propane,1-bromo heptane and benzyl chloride. The polymeric reagent was characterized by IR and thermo-gravimetric analysis. The oxidized products were characterized by FTIR and H1NMR spectral methods. The reagent was reused for the oxidation of a fresh alkyl / aryl halides and it was observed that the polymeric reagent oxidizes the compounds successfully but with little lower product yield.

Non-Isothermal Degradation and Thermodynamic Properties of Pine Sawdust

The study of non-isothermal kinetics analyzed the reactivity of pine sawdust, while the thermodynamic properties analyzed energy consumed and released from the pine sawdust. The kinetic parameters were determined by analyzing mass loss of pine sawdust components by using Thermogravimeric analyzer. The cellulose has the highest conversion rate of 9.5%/min at 610 K compared to hemicellulose and lignin, which are 5%/min at 600 K and 2%/min at 800 K, respectively. The activation Energy for cellulose, hemicellulose and lignin was 457.644, 259.876, and 89.950 kJ/mol, respectively. The thermodynamic properties included the change of Gibbs free energy for cellulose and hemicellulose, which were -214.440 and -30.825 kJ/mol respectively, their degradation was spontaneous in forward direction, while change of Gibbs free energy for lignin was 207.507 kJ/mol, which is non-spontaneous reaction. The positive value of change of entropies for the active complex compounds formed from hemicellulose and cellulose is less stable, while the active complex compounds of lignin are characterized by a much higher degree of arrangement since its change of entropy is negative. The kinetic and thermodynamic properties show that pine sawdust is a good candidate for production of char since it is easier to remove hemicellulose through thermal process.

Pyro and Kinetic Studies of Barium Oxalate Crystals Grown in Agar Gel

Single crystals of barium oxalate have been grown using gel method at ambient temperature. Thermal characteristics and kinetic parameters of barium oxalate crystals were determined by thermo-gravimetric (TG) analysis under non-isothermal heating conditions. The pyrolysis experiments were performed with increasing temperature up-to 600℃ at heating rate of 5℃, 7℃ and 10℃ in nitrogen gas atmosphere. The pyrolysis curve showed that loss of mass took place mainly in the range of 220℃ - 400℃. At higher temperature there was a significant mass loss due to decomposition of oxalates. Ozawa and Coats & Redfern methods were used to determine the apparent activation energies of material degradation. The apparent activation energies for barium oxalate crystals were obtained 187.42 KJ·mol-1 and 185.4 KJ·mol-1 for the respective methods.

Effects of Particle Size on Nitridation Kinetics of Manganese Powder

Isothermal thermo-gravimetric analysis was applied to investigate the nitridation kinetics of manganese powder with different particle sizes at 800, 900 and 1000 ℃. The apparent activation energy and nitridation kinetics equations of manganese powder with different particle sizes were obtained from unreacted shrinking core model and Arrhenius formula. It was found that the nitridation mechanism was controlied by interracial chemical reaction. The apparent activation energy and the apparent rate constant of nitridation reaction were affected by particle sizes. With the decrease of particle size, the apparent activation energy decreased whilst the apparent rate constant increased. It was suggested that the refinement of the manganese powder contributed to the increase of molar surface energy, which accounted for the lower apparent activation energy.

Synthesis and optical properties of nanostructured Ce(OH)_4

Nanocrystalline cerium hydroxide （NCs-Ce（OH）4） is a intermediate product of CeO2, synthesized successfully using a novel and simple wet chemical rout at an ambient temperature for the preparation of NCs CeO2 powder and film on mass scale for various purposes. The synthesized NCs-Ce（OH）4 was characterized using X-ray diffraction （XRD）, scanning electron microscopy （SEM）, thermo-gravimetric analysis （TGA）, Fourier transform infrared （FTIR）, UV-visible and photoluminescence （PL） spectroscopy. The average crystallite size of NCs-Ce（OH）4 has been estimated by the Scherrer equation to be 3-4 nm. The SEM examinations show that the surface texture was uniformly agglom- erated and homogeneous. Thermal analysis suggests that cerium （IV） ion is in the tetra hydrated form. Absorption and luminescence spectroscopic studies have been examined for future application in the development of optical devices.